Search results for "dispersion model"
showing 10 items of 15 documents
In situ observations of new particle formation in the tropical upper troposphere: the role of clouds and the nucleation mechanism
2011
New particle formation (NPF), which generates nucleation mode aerosol, was observed in the tropical Upper Troposphere (UT) and Tropical Tropopause Layer (TTL) by in situ airborne measurements over South America (January–March 2005), Australia (November–December 2005), West Africa (August 2006) and Central America (2004–2007). Particularly intense NPF was found at the bottom of the TTL. Measurements with a set of condensation particle counters (CPCs) with different <i>d</i><sub>p50</sub> (50% lower size detection efficiency diameter or "cut-off diameter") were conducted on board the M-55 <i>Geophysica</i> in the altitude range of 12.0–20.5 km and on board …
Temperature effect on phase state and reactivity controls atmospheric multiphase chemistry and transport of PAHs
2017
Atmospheric refrigerator increases the global transport and health risks of carcinogenic PAHs.
Volcanic plume monitoring at Mount Etna by diffusive (passive) sampling
2004
[1] This paper reports the use of diffusive tubes in determining HF, HCl, and SO2 in the volcanic plume of Mount Etna in an attempt to highlight the potential of this method in studying volcanoes. In a first application a network of 18 diffusive tubes was installed on Etna's flanks, aimed at evaluating the atmospheric dispersion of the volcanic plume on a local scale. Results showed a monotonic decrease in volatile air concentrations with distance from the craters (HF from 0.15 to <0.003 μmol m−3, HCl from 2 to <0.01 μmol m−3, and SO2 from 11 to 0.04 μmol m−3), revealing the prevalently volcanic contribution. Matching of SO2/HCl and HCl/HF volatile ratios with contemporaneous measurements a…
An evaluation of the estimation of road traffic emission factors from tracer studies
2010
Road traffic emission factors (EFs) are one of the main sources of uncertainties in emission inventories; it is necessary to develop methods to reduce these uncertainties to manage air quality more efficiently. Recently an alternative method has been proposed to estimate the EFs. In that work the emission factors were estimated from a long term tracer study developed in Ho Chi Minh City (HCMC) Vietnam. A passive tracer was continuously emitted from a finite line source placed in one side of an urban street canyon. Simultaneously, the resulting tracer concentrations were monitored at the other side of the street. The results of this experiment were used to calculate the dispersion factors an…
Modeling and simulation of dense cloud dispersion in urban areas by means of computational fluid dynamics
2011
Abstract The formation of toxic heavy clouds as a result of sudden accidental releases from mobile containers, such as road tankers or railway tank cars, may occur inside urban areas so the problem arises of their consequences evaluation. Due to the semi-confined nature of the dispersion site simplified models may often be inappropriate. As an alternative, computational fluid dynamics (CFD) has the potential to provide realistic simulations even for geometrically complex scenarios since the heavy gas dispersion process is described by basic conservation equations with a reduced number of approximations. In the present work a commercial general purpose CFD code (CFX 4.4 by Ansys®) is employe…
Atmospheric dispersion of volcanic CO 2 at Vulcano island
2001
Abstract Intensive carbon dioxide emanations occur throughout the island of Vulcano (Aeolian Archipelago, north of Sicily, Italy). The main sources of CO 2 on the island are the hot fumaroles (∼500°C) of the northern ridge of the La Fossa crater, the fumaroles of the Baia di Levante and the emission areas spread out both on the slopes of the cone and in the nearby plain. The carbon dioxide from the soil can be considered as being emitted at air temperature. In this work, CO 2 concentrations in the air over the island are estimated by means of two numerical codes. This paper takes advantage of the parallel knowledge gained from a previously written paper for SO 2 emissions from the La Fossa …
Air pollution and childhood leukaemia: a nationwide case-control study in Italy
2013
Objectives Leukaemia is the most common cancer in children, but its aetiology is still poorly understood. We tested the hypothesis that traffic-related air pollution is associated with paediatric leukaemia because of chronic exposure to several potential carcinogens. Methods The Italian SETIL study (Study on the aetiology of lymphohematopoietic malignancies in children) was conducted in 14 Italian regions. All incident cases of leukaemia in children aged ≤10 years from these regions (period 1998–2001) were eligible for enrolment. Two controls per case, matched on birth date, gender and region of residence were randomly selected from the local population registries. Exposure assessment at bi…
High Resolution Dispersion Modeling near Tunnel Exits
1996
This contribution is concerned with a critical problem which usually occurs at motortraffic tunnels within towns. All exhaust gases accumulating along the entire tunnel distance readily leave the tunnel exits in a very concentrated form. Since modern urban traffic management affords more and more tunnel constructions within highly built-up areas, a reliable calculation of the resulting immission distribution in the neighbourhood of tunnel exits is of great importance.
Axial dispersion model for solid flow in liquid suspension in system of two mixers in total recycle
2006
The measurement of residence time distribution of solid particles in solid-liquid suspension is experimentally difficult. However, the twin system approach is particularly suited for the assessment of particle RTD in flow systems as it allows overcoming some of the usual difficulties generally encountered in this kind of measurement. Twin system consists of two vessels and external piping in total recycle. Experimental results from this system can be evaluated using Z-transforms to derive particle RTD for subsequent testing of alternative flow models. Recently, the axial dispersion model was applied using the "advection diffusion equation" (sometimes called the"diffusion with bulk flow equa…
Dispersion models and air quality data for population exposure assessment to air pollution
2014
Evaluating the extent of exposure to chemicals in absence of continuous measurements of their concentration in air and direct measures of personal exposure is crucial for epidemiological studies. Dispersion models can be a useful tool for reproducing spatio-temporal distribution of contaminants emitted by a specific source. However, they cannot easily be applied to short-term epidemiological studies because they require precise information on daily emission scenarios for a long time, which are generally not available. The aim of this study was to better assess the exposure in the industrial area of Brindisi, which suffers from various critical epidemiological situations, by integrating air …